Pregnancy due date calculator
Estimate your due date from your last period, conception date, IVF transfer, or work backward from a known due date, plus your current week and key milestone dates.
Your results
Estimated due date
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Pregnancy progressWeek 0 of 40
- Estimated last period
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- Estimated conception date
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Trimester and milestones
| Trimester | Weeks |
|---|---|
| 1st trimester | Weeks 1 to 12 |
| 2nd trimester | Weeks 13 to 27 |
| 3rd trimester | Weeks 28 to 40 |
- First ultrasound (6 to 8 weeks)
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- NT scan (11 to 14 weeks)
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- Anatomy scan (18 to 22 weeks)
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- Glucose tolerance test (24 to 28 weeks)
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- Full term (37 weeks)
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How it works
A pregnancy due date calculator estimates your expected delivery date using one of several methods: the last menstrual period (LMP) via Naegele's rule (280 days from LMP, adjusted for cycle length), conception date (266 days), IVF embryo transfer date, or working backward from a due date you already know. It also shows your trimester stage and key prenatal milestone dates.
- Pick your method
Use whichever date you actually know: last period, conception, IVF transfer, or an existing due date.
- Enter the date
For LMP, also set your average cycle length if it is not 28 days.
- Read your results
Due date, current week, trimester and milestone dates update together.
How due dates are calculated
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle with ovulation on day 14. For irregular cycles, the calculator adjusts by the difference from 28 days: a 30-day cycle shifts the due date 2 days later, a 26-day cycle shifts it 2 days earlier.
The conception date method adds 266 days, since pregnancy lasts about 38 weeks from fertilization rather than 40 weeks from LMP. For IVF, a day-5 blastocyst transfer adds 261 days and a day-3 embryo transfer adds 263 days, since the embryo's age at transfer is known exactly.
Understanding trimesters
- 1st trimester (weeks 1 to 12): organ development begins; morning sickness is common; this is the highest miscarriage risk period.
- 2nd trimester (weeks 13 to 27): often called the "honeymoon period", with less nausea; baby movements are felt and the anatomy scan is performed.
- 3rd trimester (weeks 28 to 40): rapid baby growth and more frequent checkups as delivery approaches.
Before you rely on the estimate
Only about 5% of babies arrive on their exact due date; most are born within two weeks before or after. A first-trimester ultrasound is the most accurate way to date a pregnancy, typically within 5 to 7 days. Your healthcare provider may adjust your due date based on ultrasound measurements.
Frequently asked questions
How is a pregnancy due date calculated from the last period?
Naegele's rule adds 280 days to the first day of your last menstrual period and adjusts for cycle length: if your cycle is shorter or longer than 28 days, the calculator shifts the due date by the difference. A 30-day cycle shifts it 2 days later; a 26-day cycle shifts it 2 days earlier. This gives the estimated due date, which falls at 40 weeks of pregnancy.
How accurate is a pregnancy due date calculator?
Estimated due dates based on LMP are accurate to within about a week for women with regular cycles. Only approximately 5% of babies are born on their exact calculated due date. In clinical practice, an early ultrasound (8 to 12 weeks) provides a more accurate due date by measuring the embryo's actual size. The calculator's date is a useful planning estimate, not a guarantee.
How is due date calculated after IVF embryo transfer?
For IVF pregnancies, the calculator uses the embryo transfer date and the embryo's developmental stage. A day-5 blastocyst transfer adds 261 days to get the due date, because the embryo is already 5 days old. A day-3 embryo transfer adds 263 days. This is more precise than LMP-based calculation because the fertilization date is known exactly.
What are the pregnancy trimester date ranges?
The first trimester spans weeks 1 to 12, the second trimester covers weeks 13 to 27, and the third trimester runs from week 28 to birth around week 40. The calculator identifies which trimester you are currently in and shows key milestones: first ultrasound around week 8, NT scan at week 12, anatomy scan at week 20, glucose test at week 26, and full-term status starting at week 37.
I already know my due date. Can I find my likely conception date?
Yes. Choose the "Known due date" method and enter your due date; the calculator subtracts 280 days to estimate your last menstrual period and 266 days to estimate your conception date. This reverse calculation is approximate, since it assumes a standard 28-day cycle and average timing.